The Interplay Between Liver First-Pass Effect and Lymphatic Absorption of Cannabidiol and Its Implications for Cannabidiol Oral Formulations.
For highly lipophilic drugs, passage into the intestinal lymphatic system rather than the portal vein following oral administration may represent a major alternative route of delivery into the general circulation. Increasing intestinal lymphatic transport provides an effective strategy to improve oral bioavailability when hepatic first-pass metabolism is a major rate-limiting step hampering access to the systemic circulation after oral dosing. The transfer of orally administered, highly lipid-soluble drugs to the lymphatic system is mediated by their association with chylomicrons, large intestinal lipoproteins that are assembled in the enterocytes in the presence of long-chain triglycerides or long-chain fatty acids. Due to its very high lipophilicity, cannabidiol (CBD) has physicochemical features (e.g. logP = 6.3) consistent with an oral absorption mediated at least in part by transport via the intestinal lymphatic system. CBD also undergoes extensive first-pass hepatic metabolism. Formulation changes favoring diversion of orally absorbed CBD from the portal to the lymphatic circulation pathway can result in reduced first-pass liver metabolism, enhanced oral bioavailability, and reduced intra- and intersubject variability in systemic exposure. In this manuscript, we discuss (1) evidence for CBD undergoing hepatic first-pass liver metabolism and lymphatic absorption to a clinically important extent; (2) the potential interplay between improved oral absorption, diversion of orally absorbed drug to the lymphatic system, and magnitude of presystemic elimination in the liver; and (3) strategies by which innovative chemical and/or pharmaceutical delivery systems of CBD with improved bioavailability could be developed.